Table of Contents

• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Data Files
• Parameters
• Instruments
• Deployments
• Project Information
• Funding

Nitrogen and Oxygen isotopes in Nitrate (NO3) measurements from samples retrieved from CLIVAR P16S in 2005.

These data are discussed in Rafter et al., 2013. Coupled nitrate nitrogen and oxygen isotopes and organic matter remineralization in the Southern and Pacific Oceans, J. Geophys. Res. Oceans, 118, 4781-4794, doi: 10.1002/jgrc.20316.

Seawater samples between 65 S and 20 S were collected by the science crew of the CLIVAR program (CLIVAR P16S during January/February 2005).  Seawater samples between 8 S and 7N were collected by the science crew of NOAA ship R/V Ka’imimoana.  Nutrients were measured on board (nitrate, nitrite, phosphate, and silicate), and 50 mL samples were frozen.  Samples from the Chilean Margin were acquired in February 2010 and frozen, and nutrient measurements were made at Rutgers University shortly afterward.

All samples were analyzed at Princeton University for nitrate N and O isotopes using the "denitrifier" method [Sigman et al., 2001; Casciotti et al., 2002]. In this method, nitrate and nitrite are converted to N2O gas using denitrifying bacteria and the N and O isotopes of this N2O are measured on an isotope ratio mass spectrometer. These measurements are referenced to atmospheric N2 or Vienna Standard Mean Ocean Water, respectively, with analytical precision of +/-0.2% for nitrate d15N and +/-0.3% for nitrate d18O for in-house seawater-based reference material. The reported measurements are of nitrate + nitrite. Nitrite is generally less than 1% or less of the nitrate + nitrite at all stations and for simplicity the analyses are referred to below as "nitrate."

Nitrate is a ubiquitous form of biologically available nitrogen in the environment. Based on previous method development in the principal investigator's laboratory, CAREER graduate students and undergraduates investigate the nitrogen (N) and oxygen (O) isotopes of nitrate as 'tracers' of the N cycle, focusing on the marine environment. Research centers on two projects: (1) lab culture, in vitro assay, and field incubation studies of the coupled N and O isotope dynamics of nitrate assimilation and denitrification, two of the critical reactions in the N cycle; and (2) incorporation of the N and O isotopes of nitrate into numerical models of ocean circulation and biogeochemistry. These projects, in the context of the oceanic data sets generated in the principal investigator's laboratory, allow for the quantification of biogeochemical processes the signals of which are otherwise complicated by their simultaneous occurrence and by ocean circulation.

Oceanic data used in this project includes Nitrogen and delta 15N of dissolved nitrate relative to atmospheric N2 (dN15_NO3) collected during five cruises in the Southern Ocean -- in September, 1997, March, 1998, and August, 1998, February, 2001, and November 2006.  During the last two cruises, samples of Oxygen isotopic composition (18O/16O) of nitrate (d180_NO3) were also collected.

Related files and references:
DiFiore, P. J., D. M. Sigman, T. W. Trull, M. J. Lourey, K. Karsh, G.Cane, and R. Ho (2006), Nitrogen isotope constraints on subantarctic biogeochemistry, J. Geophys. Res., 111, C08016, doi:10.1029/2005JC003216.

DiFiore, P. J., D. M. Sigman, and R. B. Dunbar (2009), Upper ocean nitrogen fluxes in the Polar Antarctic Zone: Constraints from the nitrogen and oxygen isotopes of nitrate, Geochem. Geophys. Geosyst.,10, Q11016, doi:10.1029/2009GC002468.